Ethernet-based field bus systems are being increasingly used in automation technology. Based on the Ethernet protocol, these systems use an Ethernet data frame to access a connected device. However, an Ethernet data frame has a considerable overhead of data, which are needed primarily for controlling Ethernet telegrams via an Ethernet-based network.
Another disadvantage of an Ethernet-based field bus system is that each bus user must be physically equipped with an Ethernet interface, even though in many cases it is necessary to span only small distances. This results in unnecessarily high costs.
For carrying out control tasks in real time, it is known from EP 1 590 927 B1 to connect the bus user provided for the real-time application to a ring-shaped transmission path of a lower-level bus system, this ring-shaped transmission path being connected via a network coupler to a higher-level network on which Ethernet telegrams may be transmitted. The network coupler is designed in such a way that an Ethernet telegram which is received by the network via an external interface of the network coupler is relayed to an internal interface of the network coupler and is output on the ring-shaped transmission path, wherein when the Ethernet telegram passes through on the ring-shaped transmission path, each bus user connected to the ring-shaped transmission path exchanges the payload data intended for the particular bus user with the Ethernet telegram circulating on the ring-shaped transmission path. Real-time requirements may be met by reducing the response time of the individual bus users as the result of processing the Ethernet telegrams on the ring-shaped transmission path as they pass through the bus user connected thereto.
However, a disadvantage of the method described in EP 1 590 927 B1 is that the Ethernet telegram circulating on the ring-shaped transmission path contains the above-described overhead of data, which is carried along without any benefit to the lower-level bus system. Transmission bandwidth of the lower-level bus system is thus unnecessarily wasted without the ability to implement management and/or control tasks for the lower-level bus system. In addition, use of the ring-shaped transmission path results in “jitter,” which limits the maintenance of real-time requirements.